On December 22, 2009, it was announced that Aoki would not be taking on fellow DREAM fighter Tatsuya Kawajiri as had been speculated for Dynamite!! 2009, the DREAM/Sengoku New Year's Eve event, but would be fighting Sengoku Lightweight Champion, Mizuto Hirota, following the DREAM vs. Sengoku theme of most of the matches. [19]. In his pre-fight interview Aoki stated that he felt insulted with the the short notice changes as he was looking forward to battling it out with one of the world's other top lightweight competitors in Kawajiri. Aoki's opponent Hirota just came off a spectacular win over long time friend of Aoki's, Satoru Kitaoka to become the new Sengoku Lightweight champion. The fight between Aoki and Hirota was considered to be one of the main events of the night along with Satoshi Ishii vs. Hidehiko Yoshida and the K-1 bout Masato vs Andy Souwer. Aoki defeated Hirota via a brutal submission that Aoki would later title "Keiichi Sasahara 2010."[20] that broke Hirota's arm in the first round at 2:17.

"When I had his arm behind his back, I could feel it popping, I thought, 'Well, this guy's pride just won't let him tap, will it?' So without hesitation, I broke it. I heard it break, and I thought, 'Ah, there, I just broke it.' I was stopped afterward, but even if I hadn't been, continuing to break it more would have been fine by me."[21]

When the fight was stopped, Aoki gave the finger to Hirota and Hirota's corner along with crowd before leaving the ring which caused some controversy since Aoki on occasion before criticized American fighters for being disrespectful in the sport. Aoki later apologized for his behavior in his post fight interview:

"After my fight, I was excited, and so I did something rude that I should apologize for. But that showed just how excited I was over that fight."[21]